1. Electrical. An element/phenomenon of Alternating Current electricity and its sine wave. For more information, see this article, from EC&M magazine. Also check out this article: Hidden_Harmonic_Filter, written by our own STEVETERRY, published in the Spring 2008 issue of ESTA's quarterly publication, Protocol. See also triplen harmonics. 2. Acoustics/Wave Theory. Pitches multiple octaves higher than the initial tone, known as the fundamental. See http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l4d.html.